The possibility is that the MoT station may not be able to test the vehicle as presented anymore if it no longer has V5 classification "motor caravan" they may have to test it as an HGV, after all if the Police do not care what you have done to the inside then it is an HGV vehicle and I suppose they would expect to see a certificate to say that it has met HGV test standards? This could be where the " Only vehicles constructed on base chassis" comes into play i.e. coach built. As the vast amount are constructed on >3.5 ton chassis so these will be allowed the " Motor caravan" status this will of course more or less kill the self build club as building coach built is a far different story to conversion and Type approval comes into play. Maybe this is the intention to curb our right to build Motorhomes over 3.5 ton. Time will tell. ☹Phil
Ref the black emboldened comment ...
A lot more things would have to change for that to happen as the classification on the V5C has nothing to do what the MOT Station test. It may sound strange but an MOT station DO NOT look at the V5C, either on paper or on-line. And this is a deliberate policy. They test a vehicle as it is presented and not according to what it written on the V5C.
And bear in mind MOTs are done under the auspices of the DVSA and NOT the DVLA - and the DVLA and the DVSA do not talk to each other - either physically or electronically. Their Databases are totally separate and incompatible (incredible really!)
The first MOT I had done on my van conversion was as a "Motor Caravan". Before I booked it in, I asked them them to look and tell me if they would be happy to MOT as a Motor Caravan. They looked at said "no problem". I told them it was not a "Motor Caravan" on the V5C and they told me it was irrelevant.
It is this "Test as Presented" principle which is the crux behind the advice you see on a lot of Forums suggesting to people they remove Motorbikes and the like from ay internal garage spaces as the vehicle supposedly becomes a "Living Van" (which doesn't seem to even have a DVLA classification! I suppose a "Van/Side Windows" is the closest?).
If there WAS a change to make MoTs applicable to the V5C documentation, then that would probably mean that >3.5t conversions are still doable same as under 3.5t conversions, but the vehicle would just have the VOSA test instead of an MOT test. Simples.
Except ... one base vehicle type would have an issue .... Mini-Buses! >3.5t Minibuses can have either MOTs or PCVs done (my own one has had both when it was an active minibus) but once converted, I would imagine you would end up with a vehicle that might have to be a "Van/Windows" if it is refused to be a "Motor Caravan" and is not stuffed with passenger seats". Once like that, an MOT or a PCV is not applicable, and an HGV test can't be done either as there is no HGV plate so VOSA will not test. So your >3.5t ex-minibus could end up in no-mans land should this change to the MOT principle of "testing as presented" change.